1. Field of the Invention
The present invention relates to a charging member to be used in an electrophotographic apparatus. The present invention also relates to a manufacturing method for the charging member. The present invention also relates to an electrophotographic apparatus and process cartridge including the charging member.
2. Description of the Related Art
As means for charging a photosensitive member in an electrophotographic apparatus such as a copying machine or a printer, there is given a contact charging system involving bringing a charging member into contact with the photosensitive member to charge the photosensitive member. As the charging member, there is generally known one having a configuration in which an electroconductive elastic layer is formed on an electroconductive support and a surface layer is formed on the electroconductive elastic layer. A shaft made of a metal is used as the electroconductive support. A vulcanized rubber having mixed therein various additives is used for the electroconductive elastic layer in order that functions as the charging member may be fulfilled. Further, a resin or the like is used for the surface layer in order that functions such as control of an electrical resistance value and prevention of smear may be fulfilled.
The electroconductive elastic layer generally has such electroconductivity as a volume specific resistivity of about from 1×103 to 1×107 Ω·cm. In order to obtain an elastic layer having such electroconductivity, Japanese Patent Application Laid-Open No. H09-090714 discloses that an electronic conduction-type electroconductive rubber composition having blended therein electroconductive particles such as carbon black is used to form the elastic layer.
However, in the charging member including such elastic layer using a rubber or a thermoplastic elastomer, when the elastic layer is brought into abutment with the photosensitive member in a static state over a long time period, deformation that is not easily recovered (compression set) may be generated in the abutment portion. It should be noted that “compression set” is hereinafter sometimes referred to as “C set” in short. When the charging member in which the C set is generated is used for electrophotographic image formation, a defect may occur in an electrophotographic image. Herein, such electrophotographic image having a horizontal streak-like defect caused by the C set in the charging member is hereinafter sometimes referred to as “C set image.” In order to suppress generation of the C set image, there has been proposed a method involving forming on a surface of the elastic layer a high-hardness and low-friction surface layer formed of a resin material or the like (see Japanese Patent Application Laid-Open No. 2000-267394).